Electrophysiological procedures often involve recording cardiac electrical activity to determine the location of arrhythmogenic tissue causing heart rhythm abnormalities, such as atrial fibrillation, atrial flutter, ventricular arrhythmias, atrial-ventricular (AV) conduction delays or blocks, and paroxysmal supraventricular tachycardia (PSVT), for example. Treatment of such arrhythmias typically include diagnosing the source of the arrhythmia by locating its origin (“mapping”) and restoring normal heart rhythms by isolating or destroying the arrhythmia-causing sites (“ablation”).
Today, many electrophysiological medical procedures, including those involving cardiac diagnoses and treatments, are performed using minimally invasive surgical techniques, wherein one or more slender implements such as catheters or the like are inserted through small incisions into a patient's body. For ablation procedures, the treatment implement or device can include a rigid or flexible structure having an ablation implement at or near its distal end placed adjacent to the tissue to be ablated. Tissue ablation is typically undergone to thermally destroy or surgically remove arrhythmia-causing tissue. Such thermal techniques often include burning or freezing the arrhythmogenic focus or conduction defect and thus destroying the offending tissue region or structure. While radio frequency (RF) energy is a popular method for ablation, once a physician commences RF energy delivery to the subject tissue, the procedure is irreversible. No correction can be made for mapping or errors in identifying the origin of the arrhythmia.
Cooling the target tissue to a certain degree, however, does allow for the temporary interruption of electrical activity proximate such tissue. The resulting effects on the heart may then be measured, as with the mapping techniques outlined above, to confirm that the temporarily-stunned tissue is indeed the unwanted tissue that should subsequently be permanently ablated. Tissue temperatures in the range of approximately +10 to −40 degrees Celsius may be used for relatively short periods of time to cause a reversible interruption of electrical activity in either normal or arrhythmic tissue. This range may be used with mapping techniques to confirm the effects of cryotreatment and to assess heart function. Tissue temperatures less than approximately −40 degrees Celsius may be used to cause permanent interruption of electrical activity, cell death, necrosis, or apoptosis in some or all of the tissues surrounding the target region of tissue.
In light of the varied temperatures that can be provided through cryotreatment to either temporarily stun the tissue or permanently ablate the target tissue, it would be desirable to provide for the efficient and controllable operation and regulation of a cryogenic device employed for these purposes.